<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* l v h a 顺序不能换 */
        a:link{
            /* 访问前 */
            color: #000;
            text-decoration: none;
        }
        a:visited{
            /* 点击后 */
            color: orange;
        }
        a:hover{
            /* 鼠标悬停时 */
            color: red;
            text-decoration: underline;
        }
        a:active{
            /* 点击时（激活时） */
            color: green;
        } 
    </style>
</head>
<body>
    <a href="#">百度一下</a>
</body>
</html>